On September 3, 1996, about 1230 central daylight time, a Cessna A188B, privately registered, experienced a loss of engine power and was substantially damaged during a forced landing near Winona, Mississippi. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 137 aerial application flight. The commercial-rated pilot was not injured. The time of departure has not been determined. The pilot/airplane owner stated to an FAA inspector that he had completed his spray operations and was returning to his base of operation when smoke entered the cockpit. He then reduced power and the smoke dissipated, but when he reapplied power the engine did not respond. He landed in a cotton field and after touchdown with obstructions ahead, he attempted to maneuver to avoid the obstructions. The left main landing gear traveled into a depression separating the landing gear wheel, and the airplane then nosed up and came to rest upright. Examination of the airplane revealed oil externally on the fuselage and in the engine compartment area. Examination of the engine compartment revealed a hole chaffed in a flexible hose from the outlet of the oil cooler. Only 2 quarts of oil registered on the oil dipstick. The oil capacity of the engine is 12 quarts. The airplane owner/pilot stated that he is not an airframe or powerplant mechanic and he had about 2 or 3 weeks before the accident, repaired engine baffling located on the right forward side of the engine. This required loosening of "B" nuts at the engine crankcase for the inlet and outlet hoses to and from the oil cooler. After tightening of the "B" nuts for the hoses following repair to the baffle, the outlet hose was too close to a heat shield between the engine exhaust for cylinder Nos. 1, 3, and 5. The owner/pilot also stated that he performed the repair after the annual inspection which was performed on March 14, 1996. The airplane had been operated for about 50 hours since the repair to the baffle.